Kim Kardashian said she's worn a sauna suit for weight loss. They can be dangerous and even deadly, a doctor said.

• Kim Kardashian said she used a sauna suit to lose weight for the 2022 Met Gala.
• Sauna suits cause water loss through sweat, not fat loss, Dr. Spencer Nadolsky said.

Sauna suits like the one Kim Kardashian used to lose 16 pounds in three weeks ahead of the 2022 Met Gala to fit into Marilyn Monroe's dress are "dangerous" and potentially deadly, a doctor has told Insider.

To lose weight at a rate that was criticized as unhealthy by dietitians and nutritionists, Kardashian said she ate "just the cleanest veggies and protein," ran on a treadmill, and wore a sauna suit twice a day.

Sauna suits come in various forms, but are usually body suits resembling tracksuits, designed to be worn during exercise. They cause sweating by increasing body temperature, and are often used by athletes — such as boxers or wrestlers — to achieve a certain weight prior to competing.

Saunas and sauna suits work for weight loss because they make you sweat and lose fluid, obesity physician and lipid specialist Dr. Spencer Nadolsky told Insider. "They do not augment fat loss and can be quite dangerous."

People have died from using sauna suits

Nadolsky said he wouldn't recommend using sauna suits in any situation.

"People have died from using them due to dehydration," he said.

It's important to understand that our bodies regulate our fluid and electrolyte balance carefully, Nadolsky said, and excess sweating can be detrimental to both these balances.

"Staying hydrated is very important for overall health," he said. Nadolsky recommends staying hydrated while sweating by drinking fluids.

However, sauna suits appear to have benefits in certain controlled settings. A 2017 study by the American Council on Exercise found that obese or overweight people who exercised in sauna suits saw greater improvements in their aerobic fitness when compared to those who didn't.

Cedric X. Bryant, American Council on Exercise chief science officer, said in a statement at the time: "The study shows sauna suits, used safely and responsibly, may help people with obesity reap more of the health benefits of regular exercise."

But he said the real message behind the data was that exercising consistently is important.

Sauna suits cause the body to temporarily lose water, not fat

In addition to being dangerous, sauna suits only lead to weight loss through water, not fat, Nadolsky said.

Water loss isn't the same as fat loss, and the weight reduction is only temporary.

"Cutting water may change the number on the scale but it is not fat," Nadolsky said.

Excess sweat from the sauna suit and cardio, as well as cutting carbs, means Kardashian's rapid weight loss was likely mostly from water, dietitian Nichola Ludlam-Raine previously told Insider.

Fast weight loss of more than 1-2 pounds a week is not generally recommended by health professionals.

When the weight lost is water not fat, it is regained once you rehydrate or eat more carbs or salt, which cause the body to retain more water.

To lose weight healthily and safely, dietitians and nutritionists do not recommend dropping calories too low or over-restricting by cutting out food groups.

Kim Kardashian's team did not immediately respond to Insider's request for comment.